How Things Work: The Claw Game

The claw game ? you know, that game where you thought you?d grabbed a stuffed bear but now you?re mad because that worthless claw dropped it ? has ruthlessly taken 50 cents at a time from children for years. The game is fairly simple: it?s a big box packed with stuffed animals, a claw, an xy-plotter, and a spool. All you need to do is use controllers to direct the claw above a stuffed animal, and press a red button. Sounds easy...
But Mike Muszynski, a mechanical engineering student who built his own claw game at Northwestern University, says that commercial claw games are constructed to be difficult to win. ?The hardest part for most people is probably figuring out how to drop the claw when they want it,? he says. ?It?s very easy to look at the claw as it moves left and right, but much harder in the direction towards and away from you.?
When the user moves the control, a signal is sent to spring solenoid motors that move the ends of two long metal rods along a timing belt at the top edges of the box. These two metal rods crisscross in a traveler, a metal cube that upholds a spool assembly. The spool assembly is a motor attached to a shaft and spool by a large gear. When a user presses the button to drop the claw, the spool assembly lowers the claw.
?The claw uses a motor attached to a threaded rod,? said Muszynski. ?The rod is screwed into what we called the iron cross. The cross was then attached to each of the fingers. As it works, the cross does not rotate, as it?s connected to the four fingers. The motor turns the rod, and the cross moves up and down, because it?s not constrained in that direction, opening and closing the fingers.?
The claw?s fingers are often made out of plastic or aluminum in commercial machines. Because the fingers are smooth and powered by low voltages that support a weak grip, users usually have difficulty grabbing a prize. In fact, in January of 2004, a seven-year-old named Timmy Novotny had so much trouble with one claw game in Wisconsin that he climbed into the machine and became a prize himself. Firemen had to be called to rescue the child from the machine.
There are various ways that vendors can wire their claw games. Muszynski powered his machine with 24 volts and used two switches, which then attached to the motors that moved the rods. Vendors might also use a simple circuit board to direct the input electrical signals to the motors. That way, the vendors could have four directional buttons instead of switches.
The claw game?s aluminum enclosure is invariably painted with some bright, enticing words, such as ?WIN A PRIZE!? But who do they think they?re kidding? You?re not winning anything from this contraption.